Lightning strikes against wind turbines has always been a problem needing attention because of damage to the wind turbine components reduces the operation time of the wind turbine and adds to the costs of operating the wind turbine.
The trend of modern wind turbine technology has been to build still larger wind turbines, which increase the wind turbines susceptibility to lightning strikes. The wind turbine rotor blades are the components of a wind turbine, which are in greatest risk of getting struck by lightning. Systems have been developed to protect wind turbine rotor blades against lightning strikes.
Some of these systems use current conducting metal layer on the surface of the wind turbine blade tips or even blade tips made in metal. The metal layer or metal tip is connected to the internal blade down conductor and subsequently a ground potential i.e. acting as an enlarged lightning receptor.
International patent application WO 2005/031158 discloses lightning protection means where the blade tip is partly or fully made in solid metal.
Other systems usually have one or more lightning receptors placed in the surface of the rotor blade connected to an internal blade down conductor, which provides a low impedance path to ground for the lightning to follow.
An example of such system is disclosed in international patent application WO 02/48546.
However, the lightning does not always strike the lightning receptors when striking the wind turbine rotor blade. Sometimes the lightning will hit and enter into the blade tip and form a path to ground by forming an arc between the blade surface and the down conductor, even though this path to ground is higher impendent, than if the lightning had struck the lightning receptor directly. The presence of the arc inside the rotor blade tip may cause severe damage to the rotor blade tip e.g. because of the significant increase in temperature in the confined space of the rotor blade tip.
It is therefore an object of the present invention to provide a wind turbine rotor blade without the drawbacks of well known lightning protection systems and especially to provide a wind turbine rotor blade with an improved lightning protection system in relation to internal arching.
Further it is an object of the present invention to provide an advantageous method of producing a wind turbine rotor blade according to the present invention.